The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Well stimulation using a solution of reactant to dissolve formation media, e.g., acid stimulation of carbonate formations, is used to increase the production of reservoir fluids to the wellbore. The art has long sought modeling techniques and tools to optimize the rate of reactant injection.
If the injection rate is too low, the reactant is spent as soon as it contacts the medium, dissolving only the face of the medium, in a process known as “face dissolution” shown in FIG. 1A. As the injection rate is increased, “conical” dissolution occurs, as seen in FIG. 1B, where the face dissolution is still present and the wormhole is short and wide. As seen in FIG. 1C, at intermediate injection rates, a long, dominant channel running deep in the formation, known as a wormhole, is formed, which is considered the optimum enhancement for flow and is associated with the optimum injection rate. At higher rates more uniform dissolution widens the wormhole as the reactant dissolves the medium over a larger and larger region, as seen in FIGS. 1D and 1E, and a large volume of rock is dissolved by excessive reactant without significant flow improvements.
Given the importance of matrix stimulation in the oil and gas industry, a large number of models, including dimensionless models, capillary tube models, network models and continuum models, have been developed in an effort to predict behavior and optimize injection parameters. Many of these suffer from drawbacks of requiring knowledge of, difficult to obtain parameters, restriction to certain types of reaction regimes, inability to account for wormhole initiation and/or uniform dissolution patterns, requiring enormous computational power to scale to field conditions, difficulty coupling reaction and transport mechanisms, and the like. The art is desirous of modeling methods and tools that overcome one or more of these drawbacks and that can be used to better implement matrix stimulation.